title: Sensitivity of dopaminergic neuron differentiation from stem cells to chronic low-dose methylmercury exposure.
abstract: Perinatal exposure to low doses of methylmercury (MeHg) can cause adult neurological symptoms. Rather than leading to a net cell loss, the toxicant is assumed to alter the differentiation and neuronal functions such as catecholaminergic transmission. We used neuronally differentiating murine embryonic stem cells (mESC) to explore such subtle toxicity. The mixed neuronal cultures that formed within 20 days contained a small subpopulation of tyrosine hydroxylase (TH)-positive neurons with specific dopaminergic functions such as dopamine transport (DAT) activity. The last 6 days of differentiation were associated with the functional maturation of already preformed neuronal precursors. Exposure to MeHg during this period downregulated several neuronal transcripts, without affecting housekeeping genes or causing measurable cell loss. Profiling of mRNAs relevant for neurotransmitter systems showed that dopamine receptors were coordinately downregulated, whereas known counterregulatory systems such as galanin receptor 2 were upregulated. The chronic (6 days) exposure to MeHg, but not shorter incubation periods, attenuated the expression levels of endogenous neurotrophic factors required for the maturation of TH cells. Accordingly, the size of this cell population was diminished, and DAT activity as its signature function was lost. When mixed lineage kinase activity was blocked during MeHg exposure, DAT activity was restored, and the reduction of TH levels was prevented. Thus, transcriptional profiling in differentiating mESC identified a subpopulation of neurons affected by MeHg, and a pharmacological intervention was identified that specifically protected these cells.
authors.affiliation: Doerenkamp-Zbinden Chair of in-vitro Toxicology and Biomedicine, Department of Biology, University of Konstanz, D-78457 Konstanz, Germany. bastian.zimmer@uni-konstanz.de
authors.forename: Bastian
authors.initials: B
authors.lastname: Zimmer
authors.forename: Stefan
authors.initials: S
authors.lastname: Schildknecht
authors.forename: Philipp B
authors.initials: PB
authors.lastname: Kuegler
authors.forename: Vivek
authors.initials: V
authors.lastname: Tanavde
authors.forename: Suzanne
authors.initials: S
authors.lastname: Kadereit
authors.forename: Marcel
authors.initials: M
authors.lastname: Leist
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D015259:Dopamine Agents / Q000494:pharmacology; D050483:Dopamine Plasma Membrane Transport Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D053595:Embryonic Stem Cells / Q000187:drug effects*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D008767:Methylmercury Compounds / Q000633:toxicity*; D051379:Mice; D023421:Models, Animal; D009474:Neurons / Q000166:cytology* / Q000187:drug effects*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D036401:Toxicity Tests, Chronic; D015854:Up-Regulation
chemical_list: D015259:Dopamine Agents; D050483:Dopamine Plasma Membrane Transport Proteins; D008767:Methylmercury Compounds; D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; C089817:cytochrome P450TYR